The equatorial oceans were over 40°C, and largely devoid of fish.

When ecologists talk about climate change, they tend to recognize there will be winners and losers. While it could drive some species to extinction, others will migrate readily to follow their shifting habitats or adapt to the changing conditions. For the most part though, nobody's expecting we'll end up with ecosystems that are largely barren.

But a new study of the aftermath of a mass extinction event suggests temperatures once got so hot that they left our planet's equatorial regions a place of "lethally hot temperatures," where the few survivors were mostly stunted invertebrates.

As a whole, life on Earth didn't have a lot going well for it at the start of the Triassic. The previous geological period, the Permian, ended with the massive eruptions that generated the Siberian Traps and triggered the biggest mass extinction event on record: the Great Dying. The volcanic activity and subsequent ecosystem changes pumped massive amounts of carbon dioxide into the atmosphere, leaving the few survivors to face intense greenhouse warming and oceans where it was difficult to obtain oxygen.

Just how intense was the warming? The authors of a paper attempt to find out by looking at the ratio of oxygen isotopes preserved in fossils from southern China. At the time, this land mass was near the equator on the east side of Pangea, covered in the shallow seas of the Tethys Ocean.

Based on their findings, the Great Dying was accompanied by a huge increase in water temperatures in the area, which rose from 21° to 36°C over the course of 800,000 years. After a period of decline, they surged again, this time reaching at least 38°C, and possibly exceeding 40°C—that's over 100° Fahrenheit. And this was ocean water; temperatures on land were likely to have been even more extreme.

That, the authors point out, is probably hot enough to kill many plants ("few plants can survive temperatures persistently above 40°C"). This is also near the limits of what animals can survive. Things are actually worse in the ocean, where increased temperatures both put strain on the organism directly and lower the amount of dissolved oxygen available.

So, the authors turned to databases of fossil finds from that era. They found the equatorial regions were relative wastelands, even as other areas of the planet were starting to recover. Fish fossils are common in many latitudes, but "very rare" near the equator. Their relatives, the tetrapods (four-limbed vertebrates) were "generally absent between 30°N and 40°S in the Early Triassic." A group of red algae were completely missing. There are few coal deposits from this era, too, which suggests major disruptions of plant life.

What was around? Some marine invertebrates. But these were so unusually small compared to their normal sizes that scientists previously described what they called a "Lilliput effect." The authors here show this effect is only present in the equatorial regions. At higher latitudes, these species are normally sized.

The authors conclude these high temperatures complicated life's recovery from the Great Dying by making a large chunk of the planet nearly inhabitable. "Extreme global warming," they write, "may progressively force taxa to vacate the tropics and move to higher latitudes or become extinct."

Uh, not quite. From testing this in my home with water kept at 60F, 70F, 80F and 90F for a science project in high school, algae and phyto-plankton LIKE warmer ocean temperatures. It helps them to grow to a certain point.

Now, past 90F, it does start to kill them... but no one can seriously say that they think that the wide oceans are going to get to 90F and above.[/quote]

With rising CO2 concentrations, you get not only rising temperatures, but increased acidification of ocean water, so you will get simultaneous rising temperature and falling pH. This will also affect survivability of sea life. Are you taking this into consideration in your experiments? If not, why not? If so, what adjustments in pH are you making, how did you determine what the magnitude of these adjustments should be, and how are you making the adjustments?

Edit: forgot to include the quote for the first two paragraphs that I am responding to. Sorry about that.

The land record may be a sampling effect not factored out as the equatorial land regions were small in that period, but I haven't read the paper.

However the extent of found fish fossils is a clincher for me.

As for the long period of suppressed recovery of diversity (~ 5 million years at least, compared with perhaps ~ 1 million for other extinctions), other recent papers have IIRC claimed repeated environmental factors keeping the biosphere off balance.

With higher ocean temperatures would come higher concentrations of oxygen in the atmosphere.

We don't know that. Indeed, anoxic water conditions would be easier to predict from a lowering of atmospheric oxygen. I think from the abstract that is what they predict, since land vegetation was hit hard in the extinction, we know that.

karolus wrote:

Correct me if I'm wrong, but even when looking at major climate swings of the course of Earth's history, from ice ages to this, the average global temperature swing was only a few degrees, correct? I wonder if many outside of the scientific community take that into account.

As far as other issues go, warmer winters are already more beneficial to pests and pathogens.

Good point on the unfortunate effects of pests. The K-Pg impact extinction had an explosion in fungal spores.

As for climate swings you mean the mature land populated biosphere I assume. Going back to ~ 3.2 Ga bp [billion years before present] several thermometers have ~ 40 degC oceans again (but no psychrophilic eukaryotes suffering from that), and the Earth under the late heavy bombardment (LHB) ~ 4.1 - 3.8 Ga bp was again locally hotter than that despite the faint early Sun. We had ~ 70 % of today's irradiation, but initially CO2 and then methane with the expanded biosphere making up for that.

Modern whole genome methods put life most likely starting before 4 Ga bp, so generic cellular life forms can take the heat and thrive. (Generic, since this was way before the domain diversification and the modern extremophiles.) Even mesophiles according to modeling of the LHB. Good thing too since cells at that time seems to have been RNA/RNA-protein based.

And today many animals are homeotherms or at least tachymetabolic on the hotter end of the mesophilic scale. [ http://en.wikipedia.org/wiki/Warm-blooded ] It is interesting to ponder that, assuming plants wouldn't be initially hit hard, the whole biosphere may be more resilient yet again.